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In the United States, the FDA (Food and Drug Administration) requires that potential drugs be demonstrated to be effective and safe before they may be used in human beings on a large scale. This requirement is particularly true for drug candidates that are to be taken by people who are relatively healthy. The trials test the effectiveness and potential side effects of a candidate drug before it is approved by the FDA for general use.

Phase 1: In phase 1, a small number (10-100) of healthy volunteers take the drug for an initial study of safety. These volunteers are given a range of doses and are monitored for signs of toxicity.

Phase 2: In phase 2, the efficacy of the drug candidate is tested in a small number of persons who might potentially benefit from the drug. Further data regarding the drug's safety are obtained. Such trials are often controlled and double-blinded.

Phase 3: In phase 3, similar studies are performed on a larger population (thousands). This phase firmly establishes the efficacy of the drug candidate and to detect side effects that may eventually develop in a small percentage of the subjects who receive treatment.

Only after the conclusion of all three phases can a drug be approved for clinical use by the public.

Clinical Trials are usually led by a principal investigator, who is often a medical doctor. Clinical studies have a research team that may include doctors, nurses, social workers, and other health care professionals. Clinical studies can take place in many locations, including hospitals, universities, doctors' offices, and community clinics. The location depends on who is conducting the study.

Controlled studies involve a group of individuals given a placebo and a second group that is given the actual drug. These studies also tend to be double-blinded, so that neither the subjects nor the researchers know which subjects are in the treatment group and which are in the control group. This approach prevents bias in the course of the trial. After the completion of the trial, the assignments of the subjects are unsealed and the results for the two groups are compared. A variety of doses are often investigated in phase 2 trials to determine which doses appear to be free of serious side effects and which does appear to be effective.

Clinical trials tend to be extremely expensive. Costs can run from tens of millions to hundreds of millions of dollars. Extensive records and documentations are filed and subsequently compiled for submission to the FDA. The full cost of developing a drug is currently estimated to be from $400 - $800 million dollars.

According to one study, it takes an estimated 15 years for a drug to go from lab to patient.